The present invention relates to a method and apparatus for detecting fine particles suspended in a apparatus for producing semiconductor device such as semiconductor substrates and liquid crystal substrates, as well as a semiconductor device processing apparatus. More specifically, the present invention relates to a method and apparatus for performing in-situ measurements of particles suspended in a processing chamber (vacuum processing chamber) for performing processes such as thin-film deposition and etching.
Processes using plasma are widely used in semiconductor fabrication processes and liquid crystal display apparatus substrate fabrication processes, e.g., in etching apparatus.
FIG. 27 shows an example of a processing apparatus that uses plasma in the form of a parallel plate plasma etching apparatus. As shown in FIG. 27, this type of apparatus uses a high-frequency signal from a signal generator 83 to modulate the output potential from a power amp 84. This high-frequency potential is split up using a distributor 85 applied to an upper electrode 81 and a lower electrode 82 disposed parallel to each other in a processing chamber. Discharge between the two electrodes 81, 82 generates a plasma 71 from an etching gas. Etching is performed on the workpiece, e.g., a semiconductor substrate (wafer) W. The high-frequency signal can use, for example, a frequency of approximately 400 kHz.
In this plasma etching apparatus, it is known that the etching reaction product from the plasma operation is deposited on the wall surface of the plasma processing chamber or the electrodes. As time goes by, the product peels off and forms suspended fine particles. As soon as the etching operation is completed and the plasma discharge stops, these suspended fine particles drop onto the wafer to form adhered particles, leading to negative circuit properties and visual pattern defects. Ultimately, these can lead to reduced yield and reduced reliability of the elements.
Many types of apparatus for inspecting particles adhered to the surface of the wafer have been proposed and implemented, but these remove the wafer from the plasma processing apparatus to perform inspection. By the time it is known that many particles are present, the processing of another wafer is already begun. This leads to clusters of defects and reduced yield. Also, evaluations performed after processing cannot determine distribution or changes over time in particles inside the processing.
Thus, there is a need in the field of semiconductor fabrication, liquid crystal fabrication, and the like of a technology for performing in-situ real-time monitoring of contamination status in processing chambers.
The sizes of fine particles suspended in the processing chamber range from submicrons to several hundred microns. In the semiconductor field, where integration scale is growing to include 256 Mbit DRAMs (Dynamic Random Access Memory) and 1 Gbit DRAMs, the minimum circuit pattern widths is decreasing to 0.25-0.18 microns. Thus, there is a need to detect sizes of particles down to the order of submicrons.
Conventional technologies for monitoring fine particles suspended in processing chambers (vacuum processing chambers) such as plasma processing chambers include Japanese laid-open patent publication number Sho 57-118630 (background technology 1), Japanese laid-open patent publication number Hei 3-25355 (background technology 2), Japanese laid-open patent publication number Hei 3-147317 (background technology 3), Japanese laid-open patent publication number Hei 6-82358 (background technology 4), Japanese laid-open patent publication number Hei 6-124902 (background technology 5), and Japanese laid-open patent publication number Hei 10-213539 (background technology 6).
The background technology 1 discloses a vaporization apparatus equipped with: means for illuminating a reaction space with a parallel light having a spectrum different from the spectrum of self-emitted light of the reaction space; and means for receiving parallel light illumination and detecting light scattered by fine particles generated in the reaction space.
The background technology 2 discloses a apparatus for measuring fine particles that uses scattering of laser light to measure fine particles adhered to a semiconductor substrate surface and suspended fine particles. The apparatus for measuring fine particles is equipped with a laser light phase modulator generating two laser lights modulated at predetermined frequencies having identical wavelengths and mutual phase differences; an optical system intersecting the two laser lights in a space containing the fine particles to be measured; an optical detection system receiving light scattered by the fine particles to be measured in the region where the two laser lights intersect and converting the light into an electrical signal; and a signal processor extracting a signal component from the electrical signal generated by the scattered light where the frequency is identical or twice the frequency of a phase modulation signal from the laser light phase modulator and the phase difference with the phase modulation signal is constant in time.
The background technology 3 discloses a technology for measuring contamination status in a reaction container that includes a step for performing scanning illumination with coherent light and generating scattered light in the reaction container and a step for detecting the scattered light in the reaction container. The scattered light is analyzed to measure the contamination status.
The background technology 4 discloses a particle detector equipped with: laser means generating a laser light; scanner means using the laser light to scan a region in a reaction chamber of a plasma processing tool containing particles to be measured; a video camera generating a video signal of laser light scattered by particles in the region; and means for processing and displaying an image from the video signal.
The background technology 5 discloses a plasma processing apparatus equipped with: a camera apparatus observing a plasma generating region in a plasma processing chamber; a data processing module processing an image obtained from the camera apparatus to obtain desired information; and a control module controlling at least one of the following list to reduce particles based on information obtained by the data processing module: evacuating means; process gas introducing means; high-frequency potential applying means; and purge gas introducing means.
The background technology 6 discloses a fine particle sensor including: a light emitter sending out a light beam illuminating a space to be measured; a detector containing an optical detector and an optical system focusing the scattered light from the space to be measured and directing it to the optical detector, the being set up so that the optical detector generates a signal representing the intensity of the light directed toward the optical detector; a pulse detector connected to the optical detector to analyze the signal from the optical detector, and detecting pulses in the signal from the optical detector; and signal processing means containing an event detector detecting a series of pulses resulting from scattered light generated by fine particles accompanying multiple illuminations by the beam while it moves in the measurement space.
In the conventional technologies described above, a laser light is sent in through an observation window disposed on a side surface of a processing apparatus. A different observation window from the laser entry observation window is disposed on the facing surface or another side surface to allow detection of front-scattering or side-scattering of the laser. Thus, in these systems for detecting front-scattered light and side-scattered light, the illumination optical system and the detection optical system are formed as different units and two observation windows are needed to attach these. Also, optical axis adjustments and the like need to be performed for both the illumination and detection optical systems, making operation difficult.
Also, an observation window is almost always disposed on the side surface of a plasma processing chamber to allow monitoring of plasma emission and the like, but in many cases only one observation window is provided. Thus, the conventional methods that require two observation windows cannot be implemented for fabrication apparatus with a processing chamber that only has one observation window.
Furthermore, in conventional systems that detect front-scattered light and side-scattered light, the illumination beam sent into the processing chamber is rotationally scanned. Observation of fine particle generation over the entire surface of the workpiece such as a wafer requires multiple observation windows and detection optical systems, leading to significant cost increases. Also, providing multiple observation windows and detection optical systems is extremely difficult practically due to space factor restrictions.
In the semiconductor field, where integration is proceeding to the levels of 256 Mbit DRAMs and 1 Gbit DRAMs, the minimum circuit pattern width is being reduced down to 0.25-0.18 microns, creating the need to detect particles with sizes on the order of submicrons. However, with the conventional technologies, separating light scattered by fine particles from plasma emission is difficult, so these technologies have been restricted to use in measuring relatively large fine particles, while detection of fine particles with sizes on the order of submicrons is difficult.
In the present invention, an illumination optical system and a detection optical system share the use of a single observation window. An optical system formed as a single unit detects particles suspended in a processing chamber. Also, the present invention provides a method and apparatus for forming a compact illumination/detection optical system that can be attached in a limited, small space. Also, the present invention provides a highly reliable method and apparatus for precisely detecting very weak particle-scattered light. Also, the present invention provides a method and apparatus for determining particle generation over the entire surface of a body being processed, e.g., a wafer.
According to another aspect of the present invention, when a desired film-forming/processing operation is being performed on a body being processed in a processing chamber, a laser light guided by an optical fiber from an external laser light source is passed through an observation window and illuminates the inside of the processing chamber. Back-scattered light scattered by particles in the processing chamber passes through the same observation window and is received by a detection optical system. The detection signal transferred to the processing module through an optical fiber is used to determine the quantity, sizes, and distribution of the particles. The results of this are displayed on a display.
According to another aspect of the present invention, the illumination beam illuminating inside the processing chamber through the observation window is rotationally scanned horizontally and back-scattered light generated in the processing chamber is detected so that a two-dimensional distribution of particles is determined.
According to another aspect of the present invention, the illumination beam illuminating inside the processing chamber through the observation window is split into multiple beams. These multiple beams are sequentially or simultaneously illuminated and the backscattered light thereof are detected so that a two-dimensional distribution of particles is determined.
These and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings.